package com.zhuxun.dmc.user.web.rest.util;

import org.springframework.data.domain.Page;
import org.springframework.http.HttpHeaders;
import org.springframework.web.util.UriComponentsBuilder;

/**
 * Utility class for handling pagination.
 * <p>
 * <p>
 * Pagination uses the same principles as the <a href="https://developer.github.com/v3/#pagination">GitHub API</a>,
 * and follow <a href="http://tools.ietf.org/html/rfc5988">RFC 5988 (Link header)</a>.
 */
public final class PaginationUtil {

  private PaginationUtil() {
  }

  public static HttpHeaders generatePaginationHttpHeaders(Page page, String baseUrl) {

    HttpHeaders headers = new HttpHeaders();
    headers.add("X-Total-Count", Long.toString(page.getTotalElements()));
    String link = "";
    if ((page.getNumber() + 1) < page.getTotalPages()) {
      link = "<" + generateUri(baseUrl, page.getNumber() + 1, page.getSize()) + ">; rel=\"next\",";
    }
    // prev link
    if ((page.getNumber()) > 0) {
      link += "<" + generateUri(baseUrl, page.getNumber() - 1, page.getSize()) + ">; rel=\"prev\",";
    }
    // last and first link
    int lastPage = 0;
    if (page.getTotalPages() > 0) {
      lastPage = page.getTotalPages() - 1;
    }
    link += "<" + generateUri(baseUrl, lastPage, page.getSize()) + ">; rel=\"last\",";
    link += "<" + generateUri(baseUrl, 0, page.getSize()) + ">; rel=\"first\"";
    headers.add(HttpHeaders.LINK, link);
    return headers;
  }

  private static String generateUri(String baseUrl, int page, int size) {
    return UriComponentsBuilder.fromUriString(baseUrl).queryParam("page", page).queryParam("size", size).toUriString();
  }
}
